1. Field of the Invention
This invention relates to compounds useful as antioxidants and detergents in lubricating oils and methods for their manufacture and, more specifically, to overbased sulfurized phenates.
2. Setting of the Invention
Lubricating oils tend to deteriorate under normal operating conditions encountered in present-day diesel and automotive engines. Sludge, lacquer and residence materials can form and adhere to engine parts (especially piston rings, grooves and skirts) possibly having a deleterious effect on engine efficiency, operation and useful life. Commonly, additives are added to lubricating oils to reduce the formation of such harmful materials and/or to keep them suspended so that the engine parts are kept clean and operating properly. Additives which reduce the tendency of lubricating oils to form oxidation products are called antioxidants, while additives which tend to suspend oxidation products and sludges are called detergents or dispersants. It is not uncommon for certain additives to exhibit both antioxidant and detergency properties. We have found that sulfurized metal phenates are quite useful as antioxidants as well as dispersants. These phenates are generally formed with an alkaline earth metal base, such as calcium, barium, magnesium, and strontium.
The manufacture of overbased sulfurized phenates has been accomplished by several different processes. One such process involves the reaction of a phenol, sulfur and an alkaline earth metal base with carbon dioxide. The present invention relates to this type of process and is exemplified by U.S. Pat. Nos. 3,036,971 and 3,194,761, which are expressly incorporated herein by reference.
It has been found that in the manufacture of lubricating oil compositions which contain overbased sulfurized metal phenates that a haze or gel can form when the phenate is mixed with bright stock oils. We believe that this haze or gel is due to overcarbonating the phenate. In the manufacture of the phenate product, carbon dioxide is added to a reaction vessel and the amount of carbon dioxide leaving the vessel is closely monitored. When the amount of carbon dioxide leaving the vessel suddenly increases this indicates that the carbon dioxide absorption has ceased and carbonation is complete. In practice it has been found that even if the injection of carbon dioxide is stopped immediately at the end of carbon dioxide absorption, the products still tend to be overcarbonated and this can cause bright stock solubility problems. We have discovered that by undercarbonating the overbased sulfurized phenate that the bright stock solubility problems can be eliminated. One method of undercarbonating is to limit the amount of carbon dioxide absorbed. Various prior art patents disclose limiting the amount of carbon dioxide absorbed; however, none of the patents disclose limiting the amount of carbon dioxide absorbed to prevent bright stock solubility problems. Further, we have found that if the alkaline earth metal is added in a single charge or stage and then carbonated, the viscosity of the reaction product increases to a level where stirring of the reaction mixture becomes difficult and the reaction may not be complete.
U.S. Pat. No. 2,916,454 to Bradley et al. discloses limiting the amount of carbon dioxide absorbed to a molar ratio of 0.2-0.6 carbon dioxide:phenolic compound. Bradley does not disclose the use of an inorganic earth metal base, such as calcium, but requires the use of complex metal alcoholates, such as barium, magnesium or sodium. U.S. Pat. No. 3,036,971 to Otto discloses the reaction of an alkyl phenol, calcium hydroxide, sulfur, and a mutual solvent. Otto discloses limiting the amount of carbon dioxide absorbed to a molar ratio of 0.2-0.6 carbon dioxide:calcium. Nowhere is it disclosed in Otto to conduct the carbonation in stages to prevent the reaction product from becoming too viscous. Both of these patents fail to disclose the concept of limiting the amount of carbon dioxide absorbed to control bright stock solubility.
U.S. Pat. Nos. 3,178,368 to Hanneman and 3,336,224 to Allphine disclose the reaction of calcium sulfonate, a phenolic compound, mutual solvent, and a high molecular weight alcohol. The amount of carbon dioxide absorbed is limited to 0.1 to 3.0 moles of carbon dioxide per mole of phenolic compound. Nowhere is it disclosed in these patents to undercarbonate to control bright stock solubility or to add an alkaline earth metal base in stages to prevent an increase in the viscosity of the reaction product. Further, both Hanneman and Allphin require the use of high molecular weight alcohols in the reaction. The use of these alcohols is economically unattractive because the alcohols are expensive and must be distilled out of the final product before blending.
U.S. Pat. No. 3,194,761 to Fox et al. discloses the reaction of a diluent oil,, alkylphenol, hydrated lime, sulfur and a mutual solvent. Carbon dioxide is bubbled through the mixture until no more than 0.5 moles of carbon dioxide is absorbed per mole of calcium. Thereafter, an additional amount of hydrated lime is added. U.S. Pat. No. 3,350,310 to Herd et al. discloses the reaction of hydrated lime, methanol and carbon dioxide at 10.degree.-30.degree. C. Thereafter phenol sulfide and a diluent are added. The amount of carbon dioxide absorbed is limited to 0.4-0.8 moles of carbon dioxide per mole of calcium. Both of these patents fail to disclose the concept of undercarbonating to control bright stock solubility. The process of Foy et al. and Herd do not disclose the addition of an alkaline earth metal base in stages to control viscosity. Further, the process of Herd requires the use of methanol and a phenol sulfide.
U.S. Pat. No. 3,923,670 to Crawford discloses the reaction of an alkyl phenol, sulfur, an alkali metal hydroxide and ethylene glycol to which is added additional alkali metal hydroxide and carbon dioxide. In Crawford there is no limit on the amount of carbon dioxide absorbed, and thus there is no suggestion of undercarbonating to improve bright stock solubility or to carbonate in stages to control viscosity.
There exists a need for a process to manufacture overbased sulfurized phenates which can have multiple carbonation stages to control viscosity and which produces a product that has no bright stock solubility problems.